Communication signal receiver and an operating method therefor

ABSTRACT

A communication signal receiver has a plurality of components. The components are arranged along at least one signal path and comprise a filter ( 130   a-b ) for processing a received signal and averaging means ( 134   a-b ) for deriving a mean value of the signal. An output of the averaging means ( 134   a-b ) is connected to a component ( 128   a-b ) located prior to the filter ( 130   a-b ) along the signal path, so that the mean value may be selectively fed back to the filter ( 130   a-b ).

TECHNICAL FIELD

The present invention relates to a communication signal receiver with aplurality of components arranged along at least one signal path, wherethe components along the or each signal path comprise a filter forprocessing a received signal and averaging means for deriving a meanvalue of the signal. The invention also relates to a method of operatinga communication signal receiver with a plurality of components arrangedalong at least one signal path, wherein a received signal is convertedto a digital form and the signal is processed by at least one digitalfilter comprised in said plurality of components.

DESCRIPTION OF THE PRIOR ART

Communication signal receivers as set out above are used in e.g.wireless telecommunication devices, such as mobile telephones.

A generic communication signal receiver according to the prior art isshown in FIG. 4. The receiver is a homodyne receiver comprising dualcommunication channels, which are commonly known as I and Q channels.The dual-channel homodyne receiver of FIG. 4 is of a kind, which isfrequently used in contemporary digital mobile telephones, such as GSM,DCS or PCS telephones.

The receiver comprises an antenna 400 for receiving an incomingelectromagnetic communication signal, such as a TDMA signal (“TimeDivision Multiple Acces”) representing a stream of digital data symbols,which have been modulated onto two orthogonal carrier waves. Thereceived signal is fed through a bandpass filter 402, amplified in anamplifier 404 and then split into two identical signals in a splitter406. The first of these signals goes to a first signal path, where it isinitially mixed in a mixer 420 a with an intermediate frequency signal.The intermediate frequency signal is fed from a local oscillator 410 andpasses unmodified through a phase shifter 408. Similarly, the secondsignal goes to a second signal path, where it is mixed in a mixer 420 bwith the intermediate frequency signal from the local oscillator 410,once the phase of the intermediate frequency signal has been shifted by90° in the phase shifter 408.

The output of the mixer 420 a is filtered by a lowpass filter 422 a andamplified in a second amplifier 424 a. Subsequently, the signal is fedto an AD converter 426 a for sampling the signal and converting it to adigital signal comprising aforesaid stream of data symbols. The digitalsignal is filtered in a digital lowpass filter 430 a, and the digitaldata symbols contained in the signal are supplied, at a node 432 a, to adigital memory 450. An average calculator 439 a determines the meanvalue (DC level) of the digital signal and supplies the mean value to anegative input of an adder 440 a. At a positive input the adder receivesthe digital data symbols, that were previously tapped from the signalpath at node 432 a. Thus, the adder 440 a will in effect subtract thesignal mean value, as determined by the average calculator 439 a, fromthe digital signal.

Consequently, the output of the adder 440 a at the end of the firstsignal path will finally provide a first part of the stream of digitaldata symbols, that were contained in and carried by the analog signalinitially received at the antenna 400. Correspondingly, the secondsignal path, starting with a mixer 420 b and ending with an adder 440 b,will provide a second part of the stream of digital data. The stream ofdigital data symbols are subsequently used by other components in themobile telephone for producing e.g. an audible output through aloudspeaker, such as speech from a party with which the user of thetelephone is currently having a telephone conversation. Alternatively,the stream of digital data symbols may represent data messages sentbetween two computers during a data communication session.

PROBLEM

The use of digital filters 430 a-b introduces a delay in the signalpath, due to the inherent operational properties of digital filters,such as FIR (Finite Impulse Response) or IIR (Infinite Impulse Response)filters. Ideally, once the last wanted digital data symbol has beensampled, the components prior to the digital filters (such as the mixers420 a-b, the amplifiers 404 a-b, 424 a-b and the AD converters 426 a-b)should be switched to a passive or idle mode, in order to preserve powerand/or to enter a transmit mode as soon as possible.

However, switching off the receiver circuits immediately after the lastwanted data symbol has been sampled causes transient noise from thedigital filter, due to the rapid change in the DC level of the signal.Therefore, in order to avoid such generation of noise, it has beennecessary for prior art receivers, like the generic one described above,to remain active for a certain period of time after the last wanted datasymbol. By doing so, the digital filters are fed with a signal withessentially nonvarying DC-level for as long as it takes for the lastsymbol to pass through the digital filters. Obviously, this contradictsthe above objective of allowing an immediate switch to a passive mode ortransmit mode.

THE INVENTION

Therefore, it is an objective of the present invention to overcome thedrawbacks of the prior art approach set out above. In particular, thepurpose of the invention is to provide an improved communication signalreceiver of the type having a plurality of components arranged along atleast one signal path, the components along the or each signal pathcomprising a filter for processing a received signal and averaging meansfor deriving a mean value of the signal, where the improvementsparticularly lie in a more rapid switch from active to passive mode andreduced power consumption.

These objectives are achieved by connecting an output of the averagingmeans to a component located prior to the filter along the signal path,so that a mean value (or DC level) of the signal may be selectively fedback to the filter for a period of time immediately following thesampling of the last wanted data symbol. Since the filter will besupplied with a signal with no rapid change in DC level, the receivercircuits may be immediately switched off, after the last wanted datasymbol has been sampled, without generating transient noise in thedigital filter.

The objectives are also achieved by a method of operating thecommunication signal receiver, wherein a received signal is converted toa digital form and the signal is processed by at least one digitalfilter, by determining an average value of the signal, detecting anevent in the signal, and in response thereof feeding the digital filterwith the average value.

Other objectives, advantages and features of the present inventionappear from the following detailed description, from the attached patentclaims as well as from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative embodiments of the present invention will nowbe described in more detail with reference to the accompanying drawings,in which:

FIG. 1 is a schematic block diagram of a preferred embodiment of acommunication signal receiver according to the present invention,

FIG. 2 is a schematic block diagram of a first alternative embodiment ofthe present invention,

FIG. 3 is a schematic block diagram of a second alternative embodimentof the present invention, and

FIG. 4 is a schematic block diagram of a generic communication signalreceiver according to the prior art.

DETAILED DISCLOSURE

FIG. 1 illustrates a preferred embodiment of a communication signalreceiver according to the present invention. Much like the prior artreceiver of FIG. 4, the preferred embodiment of FIG. 1 is a homodynereceiver with dual communication channels, which are commonly known as Iand Q channels. The components of the receiver of FIG. 1 have beenassigned a respective three-digit reference numeral from 100 to 150. Allcomponents having a reference numeral, the two rightmost digits of whichare identical to the two rightmost digits of a corresponding componentin the prior art receiver of FIG. 4, are identical or have essentiallythe same function as said corresponding component of FIG. 4.Consequently, the antenna 100, the bandpass filter 102, the amplifier104, the splitter 106, the phase shifter 108, the local oscillator 110,the mixers 120 a-b, the lowpass filters 122 a-b, the amplifiers 124 a-b,the AD converters 126 a-b, the digital filters 130 a-b, the adders 140a-b and the memory 150 are all identical to, or have essentially thesame function as, the antenna 400, bandpass filter 402, amplifier 404,etc. of the generic prior art receiver shown in FIG. 4.

Furthermore, the receiver of FIG. 1 comprises a first average calculator134 a in the first signal path as well as a second average calculator134 b in the second signal path.

Just like the average calculators 439 a-b in the prior art receiver ofFIG. 4, the average calculators 134 a-b are arranged to receive, atinput nodes 132 a-b, the digital samples (as produced by the ADconverters 128 a-b and filtered by the digital filters 130 a-b) andderive an average or mean value of a predetermined number of recentlyreceived samples. This value, which is a time-discrete digital movingaverage value, is supplied at output nodes 138 a-b to the negativeterminals of the adders 140 a-b, in similarity with the prior artreceiver of FIG. 4. Unlike the prior art receiver, the inventivereceiver of FIG. 1 has a feedback loop starting at the respective node138 a-b and ending at a respective first input terminal of a respectivedata selector or multiplexor 128 a-b, which is located between therespective AD converters 126 a-b and digital filters 130 a-b, as shownin FIG. 1. Furthermore, a counter 136 a-b is connected to the respectiveaverage calculator 134 a-b. An output of the counter 136 a-b isconnected to a respective control terminal 129 a-b of the selector 128a-b. A second input terminal of the selector 128 a-b is connected to theoutput of the respective AD converter 126 a-b.

The operation of the average calculators 134 a-b, the counters 136 a-band the selectors 128 a-b is as follows. When the receiver is in areceive mode, i.e., receives and processes a plurality of digital datasymbols as described above, the counter 136 a controls the selector 128a, via the control terminal 129 a, to forward the stream of digital datasymbols received from the AD converter 126 a to the digital filter 130a. Meanwhile, the average calculator 134 a continuously calculates anaverage value of the last n numbers of digital data symbols,representing the DC level of the digital signal (n is a predeterminednumber of samples, such as 32-128). When it has been established, e.g.,by controller means 125, that the last wanted digital data symbol hasbeen sampled by the AD converter 126 a, the counter 136 a controls theselector 128 a to instead start forwarding the average value calculatedby the average calculator 134 a to the digital filter 130 a. During apredetermined number of symbol periods the counter 136 a maintains theselector 128 a in this state, wherein the average value fed back fromnode 138 a is supplied to the digital filter 130 a.

As is readily realized by the skilled person, the actual value of thepredetermined number of symbol periods depends on the actualimplementation of the digital filter 130 a. Furthermore, it is common touse not only one digital filter 130 a, but a series of digital filters,and the actual number of symbol periods will have to be decided afterdue consideration and testings. However, for one contemporary GSMreceiver, 11 symbol periods have proven to be a suitable number for thetime period, during which the digital filter 130 a has to be fed withaforesaid average value in order to avoid transient noise in the digitalfilter.

Since the digital filter 130 a inherently has a certain DC gain, theaverage calculator 134 a is arranged to compensate for this DC gain bymultiplying with the inverse thereof before supplying its output at node138 a.

Thanks to the provision of the average calculator 134 a, the counter 136a and the feedback loop from node 138 a to the selector 128 a, thedigital filter 130 a is guaranteed to be fed with digital data having a“correct” mean value, i.e. a DC level which is essentially the same asthe DC level of the last digital data symbols. Hence, transient noise isavoided in the digital filter, since the DC level of the digital signalexhibits no rapid change. Consequently, the receiver circuits prior tothe digital filter 130 a, e.g. the AD converter 126 a, the amplifier 124a, the lowpass filter 122 a, the mixer 120 a, etc., may be switched to apassive or idle mode immediately after the last wanted data symbol hasbeen sampled. This conserves power as well as facilitates an earlierswitch to a transmit mode.

The above discussion of the operating principle of the components alongthe first signal path is applicable to the components along the secondsignal path, i.e. the second average calculator 134 b, the secondcounter 136 b, the second selector 128 b, etc. As an alternative, sincedata symbols are received simultaneously and at equal rate on bothsignal paths, the first and second counters 136 a-b may be combined intoa single counter, which is shared between both signal paths.

An alternative embodiment of the inventive communication signal receiveris shown in FIG. 2. All components having a reference numeral, the lasttwo digits of which are equal to the last two digits of a correspondingcomponent in the prior art receiver of FIG. 4, are identical or haveessentially the same function. In contrast to FIG. 1, the averagecalculators 239 a-b of FIG. 2 have no means for feeding back a meanvalue to the digital filters 230 a-b; the average calculators 239 a-bonly have their “normal” function as described above for the prior artreceiver of FIG. 4. Instead, the embodiment of FIG. 2 comprises anintegrator 234 a-b for each signal path. The integrator 234 a-b isconnected to the respective signal path between a selector 228 a-b and adigital filter 230 a-b. The selector 228 a-b is identical to or has thesame function as the selector 128 a-b described with reference to FIG.1. Furthermore, the FIG. 2 embodiment comprises a counter 236 a-b havingan input connected to the respective integrator 234 a-b. An output ofthe counter 236 a-b is connected to a control terminal 229 a-b of therespective selector 228 a-b.

The purpose of the integrator 234 a-b is to filter out the DC level(i.e. the average value) of the digital signal and to feed back thisaverage value, via an output terminal 238 a-b, to the selector 228 a-b,once the last wanted digital data symbol has been sampled by the ADconverter 226 a-b. The integrator 234 a-b may for instance beimplemented as a filter having the following filter equation:y(n)=αy(n−1)+(1−α)x(n), where α is a constant which has to be tuned andset in view of the actual application. However, other FIR or IIR filterswith appropriate lowpass characteristics may be used instead of thesimple integrator defined by the discrete differential equation above.

Consequently, the main operating principle of the embodiment of FIG. 2is essentially the same as that of the FIG. 1 embodiment; an averagevalue representing the DC level of the digital signal is derived and fedback to the digital filter 230 a-b for a predetermined number of symbolperiods immediately after the last wanted digital data symbol has beensampled, thereby avoiding rapid changes in the DC level of the signaland generation of unwanted transient noise.

FIG. 3 illustrates another alternative embodiment of the presentinvention. Just like FIGS. 1 and 2, all components in FIG. 3 with areference numeral, the last two digits of which correspond to the lasttwo digits of a corresponding component in the prior art receiver ofFIG. 4, are identical or have essentially the same function. Contrary tothe embodiments of FIGS. 1 and 2, the alternative embodiment of FIG. 3solves the problem in the analog domain rather than the digital domain;an integrator comprising a capacitor 334 a-b and a selector 328 a-bfilters out the DC level of the analog signal and stores the result as avoltage across the capacitor 334 a-b. Controller means 325 is arrangedto detect the presence of the last wanted digital data symbol at the ADconverter 326 a-b and to control the selector 328 a-b to switch from afirst state, where the selector 328 a-b is open and the capacitor 334a-b is disconnected from the first and second signal paths respectively,to a second state, where the selector 328 a-b is closed and thecapacitor 334 a-b is connected to the first and second signal paths,respectively, between the amplifier 324 a-b and the AD converter 326a-b. When the selector 328 a-b is in its second state, the output 338a-b of the respective capacitor 334 a-b is supplied to the digitalfilter 330 a-b through the respective AD converter 326 a-b, so that thedigital filter 330 a-b is supplied with a signal with no rapid change inDC level immediately after the last wanted digital symbol has beensampled by the AD converter 326 a-b. The receiver components prior tothe capacitor 334 a-b and selector 328 a-b, i.e., amplifier 324 a-b,lowpass filter 3223 a-b, etc., may be turned off or switched to apassive/idle mode at the same time.

The invention has been described above with reference to preferred andalternative embodiments. This disclosure has exemplifying but notlimiting purposes; the scope of the present invention is only limited bythe definitions in the appended independent patent claims. Inparticular, the present invention is equally applicable also to otherreceiver types not mentioned herein, such as receivers having other thantwo channels or signal paths and/or employing more than one digitalfilter per signal path.

What is claimed is:
 1. A communication signal receiver for enablingswitching from an active mode to a passive mode in order to reduce powerconsumption, the receiver comprising: a plurality of components arrangedalong at least one signal path, the components along the signal pathcomprising a filter for processing a received signal and averaging meansfor deriving a mean value of the signal, wherein an output of theaveraging means is connected to a selector located prior to the filteralong the signal path, and control means in communication with theselector, the control means for detecting an event in the signalindicative of a last data symbol and responsive thereto controlling theselector so as to cause the selector to supply the mean value comprisinga DC level to the filter in response to detection of the event in thesignal so as to enable components arranged prior to the selector alongwith signal path to be switched from the active mode to the passivemode.
 2. A communication signal receiver according to claim 1, whereinan input of the averaging means is connected to an output of the filter,and wherein the filter comprises a digital filter.
 3. A communicationsignal receiver according to claim 1, wherein an input of the averagingmeans is connected to the selector (228 a-b) located prior to the filter(230 a-b) along the signal path.
 4. A communication signal receiveraccording to claim 1, wherein said selector comprises: a selector inputoperatively connected to the output of the averaging means; a selectoroutput operatively connected to an input of the filter; and a selectorcontrol terminal operatively connected to counter means for controllingwhether data received at the selector input is to be supplied at theselector output.
 5. A communication signal receiver according to claim1, further comprising an A/D converter for converting a received analogsignal to a digital signal.
 6. A communication signal receiver accordingto claim 5, wherein the averaging means (134 a-b) is located after theA/D converter along the signal path.
 7. A communication signal receiveraccording to claim 5, wherein the averaging means (334 a-b) is locatedprior to the A/D converter along the signal path.
 8. A communicationsignal receiver according to claim 7, wherein the averaging means (334a-b) comprises a capacitor.
 9. A method of operating a communicationsignal receiver with a plurality of components arranged along at leastone signal path, wherein a received signal is converted to digital formand is processed by at least one digital filter in said plurality ofcomponents, in a manner so as to enable switching from an active mode toa passive mode, the method comprising: determining an average valuecomprising a DC level of the signal; detecting an event in the signalindicative of a last data symbol; and in response to detecting saidevent, feeding said at least one digital filter with said average valuecomprising the DC level in order to enable switching of component(s)arranged prior to the selector from the active mode to the passive modein order to reduce power consumption.
 10. A method according to claim 9,wherein said event is the presence of a certain digital data symbol at acertain component (126 a-b) prior to said digital filter (130 a-b) alongsaid signal path.
 11. A communication signal receiver comprising: aplurality of components arranged along at least one signal path, thecomponents along the signal path comprising a digital filter forprocessing a received signal and averaging means located downstream ofthe filter for deriving a mean value of the signal, wherein an output ofthe averaging means is connected via a feedback loop to a selectorlocated prior to the filter along the signal path, and a controller incommunication with the selector, the controller for detecting an eventin the signal and causing the selector to supply the mean value to thefilter in response to detection of the event in the signal so as toenable components located prior to the selector along the signal path tobe switched from an active mode to a passive mode.
 12. The receiver ofclaim 1, wherein the averaging means is located downstream of thefilter, and an output of the averaging means is connected to theselector via a feedback loop.
 13. The method of claim 9, wherein anaveraging means is located downstream of the filter, and an output ofthe averaging means is connected to a selector via a feedback loop. 14.A communication signal receiver comprising: a plurality of componentsarranged along at least one signal path, the components along the signalpath comprising a filter for processing a received signal and averagingmeans for deriving a mean value of the signal, wherein an output of theaveraging means is connected to a selector located prior to the filteralong the signal path, and control means in communication with theselector, the control means for detecting an event in the signalindicative of a last data symbol and responsive thereto controlling theselector so as to cause the selector to supply the mean value comprisinga DC level to the filter in response to detection of the event in thesignal.
 15. A method of operating a communication signal receiver with aplurality of components arranged along at least one signal path, whereina received signal is converted to digital form and is processed by atleast one digital filter in said plurality of components, the methodcomprising: determining an average value comprising a DC level of thesignal; detecting an event in the signal indicative of a last datasymbol; and in response to detecting said event, feeding said at leastone digital filter with said average value.